The study was carried out in light of the ongoing heated debate about the public health benefits of e-cigarettes and their potential impact on teenagers. It said it may be beneficial to restrict teenagers' access to e-cigarettes.

For the study, the researchers quizzed 2,338 teenagers at seven high schools in 2013, and then again a year later, about their vaping and smoking activities.

In 2013, the teenagers, all of whom resided in Hawaii, were ninth and 10th graders, with an average age of just under 15 years.

They were asked in depth about the frequency of their e-cigarette and tobacco use - from never, through a few times a year, right up to daily - at both time points.

Factors known to influence uptake of smoking, such as home environment, parental educational attainment, and degree of rebelliousness were also assessed by the survey.

The results showed that those teenagers who had used e-cigarettes in 2013 were almost three times more likely to have started smoking a year later than those who had not vaped at the time of the first survey.

But regular smoking was linked only to higher levels of e-cigarette use to start with, findings showed.

The research was recently published online in the journal Tobacco Control.